The present invention relates generally to devices and methods for providing electrical connection between two electronic components. More specifically, the present invention relates to a socket contact configured to establish electrical communication between a semiconductor die and a test device as well as methods for forming the socket contact.
Testing a semiconductor die often involves establishing an electrical connection between testing equipment and the circuitry of a die. Testing may be performed on an unpackaged die that has been singulated from a semiconductor wafer, on a section of dice that are still part of the wafer, or on all of the dies on a wafer. Moreover, a bare die that has undergone packaging steps may also be tested. One example of such a die is a xe2x80x9cflip chip,xe2x80x9d wherein conductive material, such as solder balls, is attached directly to the bond pads or electrical traces formed in the surface of the die; the die is then xe2x80x9cflipped,xe2x80x9d or mounted face down, so that the solder balls may connect with contact members of another device. Another example is a xe2x80x9cchip scale package,xe2x80x9d which includes a die along with one or more package elements, such as encapsulating material in the form of thin protective coatings formed of glass or other materials bonded to the face and back side of the die; in addition, solder balls may be attached to electrical traces in the surface of the die or directly to the die""s bond pads through openings in the encapsulating material. A Ball Grid Array (BGA) serves as yet another example that involves even more packaging: the die is wire bonded to the top of a substrate and encapsulated, and solder balls are bonded to electrical traces at the bottom of the substrate that lead to the wire bonds.
The device to be tested will hereinafter be referred to as an integrated circuit chip, or IC chip, regardless of the singulation or packaging state of the die that forms all or part of the IC chip. One method of testing the IC chip involves placing the chip into a socket, which comprises a body with holes that span through the body. These holes house contacts that are aligned with electrical contact points of the IC chip. For purposes of explanation only, it will be assumed that the contact points of the IC chip are solder balls. Often, the socket includes a lid that, when closed, pushes the solder balls of the IC chip against the heads of the socket""s contacts. Once the IC chip has been inserted, the socket is then plugged into a printed circuit board (PCB). This insertion often involves a biasing force in the opposite direction of the lid""s pushing force. To ensure electrical communication between the IC chip and the PCB without the risk of breaking the socket contacts, the socket contacts are configured to be resilient to the compression resulting from these forces. One such configuration for doing so involves the use of xe2x80x9cpogo pinxe2x80x9d contacts. A pogo pin can comprise an electrically conductive inner shaft, an electrically conductive outer shell concentric to the inner shaft and defining the head of the contact, and an electrically conductive spring between the inner shaft and outer shell. When the pogo pin undergoes compression, the inner shaft is pushed into the outer shell despite the spring""s bias. Ideally, signals received at the head of the outer shell will conduct through the spring to the inner shaft and onward to devices that may be connected to the inner shaft. However, such a design allows for unneeded electrical communication along the entire surface of the outer shell.
As an alternate configuration, buckle beams may be used. Buckle beams are essentially a thin, somewhat rigid length of conductive material that will buckle in response to compression from the IC chip and the PCB being pushed toward each other. The problem with buckle beams is that the holes housing the beams must be wide enough to accommodate the horizontal motion of the beams as they buckle. The buckling space required limits the density of beams per unit area that can be achieved. In addition, buckle beams tend to rotate during buckling. Thus, in certain aspects, pogo pins and buckle beams run contrary to the need in the art for electrical contacts that require minimal space and material.
Returning to the testing process, the PCB with the connected socket is placed in a chamber, wherein the IC chips are tested while subjected to an elevated temperature. Such testing is referred to as burn-in testing. The socket""s contacts provide electrical communication between the IC chip and signals sent through the PCB from the test equipment. Once the test is complete, the chip is removed from the socket. IC chips which do not pass the testing are discarded, and chips that pass may undergo further testing and ultimately be used as components in electronic devices.
Further testing and use of these chips, however, depends upon the ability of the solder balls to continue to function after their interaction with the socket""s contacts. Prior art socket contacts have heads that are configured through their flexibility to actively exert a force against the chip""s solder balls, wherein the force is generally transverse to the biasing force that pushes the chip into the socket. The effect of this transverse force is to pinch the solder balls, thereby severely damaging them and making further communication with the chip difficult. Such socket contacts include the aptly named xe2x80x9cpinch contactxe2x80x9d found in the Series 655 OTBGA Burn-in/Test Socket sold by Wells Electronics. Another series 655 OTBGA Socket by Wells uses a Y-shaped contact. The Y-shaped contact is further described in U.S. Pat. No. 5,545,050, by Sato et al., indicating that the head of the Y-shaped contact is flexible, which allows it to xe2x80x9csnuglyxe2x80x9d accommodate a hemispherical conductor of an IC package. (Sato at col. 4, In. 25-30.) Thus, the Y-shaped contact continues the tradition of applying a pinching action to the electrical contacts of a device.
Still other examples of contact heads are illustrated by references from Interconnect Devices, Inc. (IDI). Among the examples are plunger probe tips having crown-shaped heads, whose sharp prongs tend to gouge the surface of the chip""s contact, be it a solder ball or flat pad. In addition, IDI discloses a concave tip that might accommodate hemispherical chip contacts such as solder balls, but may provide insufficient electrical communication for other contacts, such as those configured as flat pads.
Thus, in addition to the needs in the art discussed above concerning the body of an electrical connector, there is also a need in the art for an electrical connector having a head that reduces the damage to the electrical contacts of IC chips during connection and is configured to accommodate more than one type and size of chip contact. More specifically, there is a need in the art for a socket contact that minimizes the damage to various IC chip contacts during IC chip testing.
Accordingly, the current invention provides electrical contacts as well as methods for forming them. One preferred embodiment comprises a contact as part of a socket used for testing semiconductor dice, wherein the contact has a head that defines a recess, and the head is coupled to an elongated conductive body configured to fit within a socket. More specifically, the head comprises a portion defining the perimeter of the head, with other portions of the head lower than the perimeter. In one exemplary embodiment, this head takes the form of a planar ring with a sidewall sloping downward from the ring toward the central axis running the length of the contact. This sidewall transitions to a generally planar section that is parallel to, yet lower than, the perimeter ring. Various preferred embodiments address varying degrees of transition and planarity of the portions of the contact head.
Other preferred embodiments address the body of an electrical contact, including one embodiment comprising a head, a shaft, and a spring coupling the head to the shaft. In a more specific embodiment, the spring""s coils define circles of differing circumferences. Another exemplary preferred embodiment comprises a metallic tube for the contact body, wherein the tube defines at least one slit. Yet other preferred exemplary embodiments address silicon contacts and methods for forming them. Specifically, semiconductor fabrication techniques are used to define an array of silicon contacts, and the contacts are singulated while maintaining their alignment within the array.
Still other preferred embodiments include the recessed contact head as described above in combination with the contact bodies just described. These embodiments include methods and devices wherein the head is formed separately from the body and attached thereto, as well as methods and devices wherein the head is integral to the body.